Magnetic flowmeters (or mag meters) measure flow by Faraday induction, an electromagnetic effect. The magnetic flowmeter energizes one or more coils which generate a magnetic field across a section of a flowtube assembly. The magnetic field induces an electromotive force (EMF) across the flow of conductive process fluid through the flowtube assembly. The resulting potential developed across the conductive fluid is measured using a pair of electrodes that extends into the flowing process fluid. Alternatively, some magnetic flowmeters employ capacitive coupling between the electrodes and the process fluid such that the EMF can be measured without direct contact. In any event, the flow velocity is generally proportional to the induced EMF, and the volumetric flow is proportional to the flow velocity and the cross sectional area of the flowtube.
Magnetic flowmeters are useful in a variety of fluid flow measurement environments. In particular, the flow of water-based fluids, ionic solutions and other conducting fluids can all be measured using magnetic flowmeters. Thus, magnetic flowmeters can be found in water treatment facilities, beverage and hygienic food production, chemical processing, high purity pharmaceutical manufacturing, as well as hazardous and corrosive fluid processing facilities. Magnetic flow meters are often employed in the hydrocarbon fuel industry, which sometimes employs hydraulic fracturing techniques utilizing abrasive and corrosive slurries.
Magnetic flowmeters can be specified with a variety of different lining and/or electrode materials to suit the application for which the magnetic flowmeter is employed. Examples of lining materials include polytetrafluoroethylene (PTFE); ethylene tetrafluoroethylene (ETFE); PFA; polyurethane; neoprene; and linatex rubber, as well as other materials. Electrodes may be constructed from any suitable material including 316 L stainless steel; nickel alloy 276; tantalum; platinum/iridium blends; titanium; as well as other suitable materials.
Fluoropolymer lining materials such as PTFE, ETFE, and PFA are often selected for superior resistance to chemical attack and/or high temperature operation. In at least some applications, fluoropolymer-based liners are being subjected to increased application demands. For example, in the oil and gas industry, some fluoropolymer liners are being subjected to higher pressures and/or temperatures. Such conditions create a challenge in designing and manufacturing robust magnetic flowmeter devices with fluoropolymer liners. This is because at least some fluoropolymers, such as PTFE, experience “cold flow” where the lining material expands and contracts under pressure and temperature. Such expansion/contraction can cause the process fluid to leak.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the disclosed subject matter.